Digital Subscriber Line (DSL) is a high speed data transmission technology by means of an Unshielded Twisted Pair (UTP). DSL technologies include Asymmetric Digital Subscriber Line (ADSL), Very High Bitrate Digital Subscriber Line (VDSL), ISDN (Integrated Services Digital Network) Digital Subscriber Line (IDSL), Single-pair High-speed Digital Subscriber Line (SHDSL), Asymmetric Digital Subscriber Line 2 (ADSL2), Asymmetric Digital Subscriber Line 2 Plus (ADSL2+), and Very High Bitrate Digital Subscriber Line 2 (VDSL2).
Except IDSL and SHDSL which are based on baseband transmission, all the above DSL technologies (sometimes referred to as xDSL hereinafter) adopt passband transmission with frequency division multiplexing so that DSL and Plain Old Telephone Service (POTS) coexist in one twisted pair, where DSL uses the higher band and POTS uses the baseband portion below 4 kHz. The POTS signal and DSL signal are split or combined by means of a splitter/combiner. xDSL with passband transmission uses Discrete Multi-Tone Modulation (DMT) for modulation and demodulation. A system providing multiple DSL access is a DSL Access Multiplexer (DSLAM). A reference model of the xDSL system is shown in FIG. 1, including a user-side xDSL transceiver (DSLAM) 120 and a network-side xDSL transceiver (DSLAM) 150. The DSLAM 120 includes a user-side transceiver unit 121 and a splitter/combiner 122. On the uplink, the user-side transceiver unit 121 receives and amplifies a DSL signal from a computer 110 and sends the amplified signal to the splitter/combiner 122. The splitter/combiner 122 combines the DSL signal from the user-side transceiver unit 121 and a POTS signal from a phone terminal 130; the combined signal is transmitted along a UTP 140 and received by a splitter/combiner 151 of the network-side DSLAM 150; the splitter/combiner 151 splits the received signal and sends the POTS signal to a Public Switched Telephone Network (PSTN) 160 and sends the xDSL signal to a network-side transceiver unit 152 of the DSLAM 150; the network-side transceiver unit 152 amplifies the received signal and sends the signal to a Network Management System (NMS) 170. On the downlink, the signal is transported in the reverse direction.
In recent years, with the wide application of DSL technologies, especially ADSL1, ADSL2/2+, VDSL and VDSL2, DSL lines are increasing abruptly in networks of operators. Maintaining the DSL lines to assure the quality of service (QoS) operations, diagnosing and analyzing line failures quickly, and optimizing the DSL lines for better line stability become important.
In the existing Dynamic Line Management (DLM), DSL adjustment technologies include adaptively adjusting the proportion of R and N bytes in Forward Error Correction (FEC) code words to improve line stability. The adjusting process is as follows:
In FEC code words, R stands for the number of redundant bytes and N stands for the total number of bytes. The number of correctable bytes in FEC cord words is half the number of redundant bytes, that is, R/2. The current bit error ratio is monitored and calculated in DSL, for example, by calculating the FEC count in the counter and the total number of sent bytes within a certain period of time, for example, in a 15-minute window. The formula is:
  e  =                    Error        ⁢                                  ⁢        bytes        ⁢                                  ⁢        received                    Total        ⁢                                  ⁢        of        ⁢                                  ⁢        bytes        ⁢                                  ⁢        sent              .  By adjusting the ratio of R and N, it is assured that
      R          2      ⁢                          ⁢      N        ≥  eand errors on the DSL line can be completely corrected. The stability of the line is therefore improved. In practice, however, it is infeasible for a DLM to improve line stability by adjusting the ratio of R and N, because R and N are not standard Management Information Base (MIB) parameters and not open to third-party applications. Only MIB-defined parameters can be used by third-party applications. Due to the lack of support by the MIB, the error correction capability cannot be updated dynamically with the bit error ratio to adapt to a complex environment. Therefore, the adjustment solution in the prior art cannot diagnose and clear DSL network defects quickly to improve line stability of the network.